1. Field of the Invention
This invention generally relates to doctors used in papermaking machines, and relates in particular to an improved doctor blade holder that is readily separable from and attachable to the doctor blade and removable from the papermaking machine for cleaning, inspection and repair.
2. Description of the Prior Art
Papermaking machines typically include a series of large rotating cylinders that variously form, squeeze and dry paper during its manufacture. The surfaces of these cylinders attract debris from the manufacturing process that must be removed to maintain product quality and process stability. Cleaning these roll surfaces is accomplished using devices commonly known as doctor assemblies. A doctor assembly typically includes a doctor blade, a doctor blade holder and the doctorback. The doctor blade should be perfectly flat, straight and have its longest axis parallel with the associated roll axis, and its composition must be compatible with the roll to be doctored.
The blade holder in concert with the doctor blade should exert a uniform designated load pressure on the roll surface. The blade holder holds the blade firmly against the roll, accommodates roll irregularities, and within limits, compensates for thermal expansion. The doctor back serves as the support structure for the doctor blade holder, and may be pivotally mounted on an axis that is also parallel with the roll axis. A loading mechanism may also be employed to bias the doctor blade against the roll.
In certain doctor assemblies, the blade holder may further include a top pressure plate (which holds the doctor blade), that is pivotally coupled to the doctor back via mounting hardware. The axis of rotation of this pivotal attachment is also parallel with the axis of rotation of the roll. The system may further include loading and unloading pneumatically controlled tubes on either side of the axis of rotation of the pivotal attachment of the top pressure plate to the mounting hardware attached to the doctor back. The loading and unloading tubes are for selectively advancing the doctor blade toward or away from the roll.
For example, U.S. Pat. No. 5,980,692 discloses a doctor assembly 10 that includes a doctor blade 14 that is attached to a blade holder 16 that is coupled to a doctor back 18 for doctoring a roll 12 as shown in FIG. 1. The doctor back 18 is pivotally coupled (about axis A2) to a loading mechanism 20. The blade holder 16 also includes fluid actuated unloading and loading tubes 30 and 32 respectively on either side of a pivotal attachment (A3) of a top pressure plate 34 (to which the doctor blade 14 is attached) to mounting hardware that is coupled to the doctor back 18 as further shown in FIG. 2.
The tubes 30 and 32 are supported by a tray 26 that holds the tubes in place, bracket 28 is attached to the tray 26, and the tray 26 is attached to the shelf 50 via fasteners that pass through holes provided in the tray 26. A depending bracket 36 that is welded or bolted to the top pressure plate 34 is pivotally attached to the bracket 28 as shown at A3 in FIG. 2. The bracket 28 is typically welded to the tray 26. Due to the harsh papermaking environment, tube trays are typically constructed of corrosion resistant materials, typically a 300 series stainless steel.
Assembling the blade holder 16, however, is a laborious process requiring great care in alignment and welding of the several brackets. There is a need, therefore, for an improved tube tray for a blade holder for a doctor blade assembly that is more efficient and economical to assemble.